Add DOI

README.md

@@ -6,6 +6,7 @@ Did I Find It?
 [![Docker Pulls](https://img.shields.io/docker/pulls/moeyensj/difi)](https://hub.docker.com/r/moeyensj/difi)  
 [![Python 3.7+](https://img.shields.io/badge/Python-3.7%2B-blue)](https://img.shields.io/badge/Python-3.7%2B-blue)
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+[![DOI](https://zenodo.org/badge/152989392.svg)](https://zenodo.org/badge/latestdoi/152989392)
 
 ## About
 `difi` is a simple package that takes pre-formatted linkage information from software such as [MOPS](https://github.com/lsst/mops_daymops), [pytrax](https://github.com/pytrax/pytrax), or [THOR](https://github.com/moeyensj/thor) and analyzes which objects have been found given a set of known labels (or truths). A key performance criteria is that `difi` needs to be fast by avoiding Python for loops and instead uses clever `pandas.DataFrame` manipulation.